The invention relates generally to heating systems primarily adapted to providing heated air to a space to be heated, such as a building or on enclosed portion thereof. More specifically, the invention relates to such a heating system fueled by a gaseous fuel.
Previous conventional forced-air heating systems for residential or commercial buildings, or for enclosed portions thereof, have included furnaces that burn a mixture of fuel and air in order to produce heat. Heat exchangers are included for transferring the heat from such combustion to an air flow system that is circulated through the heated space and then returned to the heat exchanger. Such conventional furnace systems have been found, however, to be wasteful in terms of their use of the thermal energy available from the combustion process, largely because exhaust gases are discharged into the atmosphere at considerably high temperatures, frequently in excess of 300 F. (149 C.), which is well in excess of the desired room temperature in the space to be heated.
Even the best of the above-described conventional furnace systems are estimated to waste at least fifteen percent to twenty percent of the gross heating value of the fuel consumed when operating at steady state conditions. Such waste of thermal energy is further compounded by the fact that when the furnace and the circulating fan of such a conventional heating systems are shut off in response to a signal from a thermostat in the heated space, the typical draft-type chimney continues to draw warm air from the furnace and from inside the building and then discharges such warm air to the atmosphere. Then when the thermostat again calls for heat, the system must restart and warm up before being capable of supplying heated air. In the northern states of the United States, this on/off cycling operation is estimated to occur over twenty thousand times per year in a typical forced-air heating system, thus resulting in an overall loss or waste of thermal energy estimated to be approximately forty percent of the available heating value of the fuel consumed.
In addition to the above disadvantages, such conventional heating systems have become economically unfeasible in large residential or commercial structures requiring very high draft-type chimneys. Because of the low cost effectiveness of the construction and maintenance of such large chimneys, such heating systems have frequently been constructed and installed on the roof of such buildings, therefore complicating their installation and increasing their cost. Alternately, especially in multi-tenant or multi-dwelling residential or commercial buildings, electric heating systems have been installed in order to reduce the initial construction cost, allow individual heating control for multiple units of the building, and eliminate the need for the building management to account for, and separately re-bill, the cost of each unit's share of the overall cost of operating a centralized heating system. Such alternate electric heating systems have included electric resistance-type heating units or heat pumps, for example, but suffer the disadvantage of being relatively expensive to operate in comparison with heating systems fueled by gaseous fuels, such as natural gas.
Because of the above-discussed disadvantages and shortcomings of conventional forced-air heating system and of typical electric heating systems, one of the primary objects of the present invention is to provide a forced air heating system, preferably fueled by a gaseous fuel, that effectively uses a much higher percentage of the available heating value of the fuel being consumed and that more effectively recovers a high percentage of the thermal energy present in the exhaust gases discharged to the atmosphere.
Another object of the present invention is to provide such a heating system that does not require a conventional chimney or other draft-type exhaust gas discharge conduit.
Another object of the present invention is to provide a heating system that maximizes the control over the function of the heating system and operates at a lower thermal energy input, but that operates for longer periods of time, thereby minimizing the number of on/off cycles required to maintain a desired temperature in the heated space, thereby maximizing the efficiency of the heating system.
Still another object of the present invention is to provide a heating system that employs a separate system for air circulating at a relatively low velocity to and from the heated space and separate high-velocity air system for transferring the heat of combustion to the air supplied to the heated space, as well as providing separate pressurized combustion air and fuel supply systems that forcibly convey combustion exhaust gases out of the heating system.
In accordance with one aspect of the present invention, a heating system for heating a space generally includes an air heating sub-system with a relatively compact combustion chamber adapted for burning a mixture of combustion air and fuel in order to produce heat, a separate cold air supply sub-system for conveying cold air from the heated space to the air heating sub-system, a combustion chamber heat exchanger in fluid communication with the cold air supply sub-system for transferring heat from the combustion chamber to the cold air withdrawn from the heated space by the cold air supply sub-system, and a separate air circulating sub-system for withdrawing cold circulating air from the heated space. The heating system also preferably includes an air mixing chamber in fluid communication with both the combustion chamber heat exchanger and the air circulating sub-system for mixing heated air with cold circulating air in order to provide heated circulating air to the heated space.
In accordance with another aspect of the present invention, the heating system includes a combustion air supply sub-system having a combustion air compressor for supplying the combustion air to the combustion chamber at an elevated pressure, a gaseous fuel supply sub-system having a gaseous fuel compressor for conveying gaseous fuel from a gaseous fuel source to the combustion chamber at an elevated pressure substantially equal to the elevated pressure of the combustion air, with the pressure of the combustion air and the gaseous fuel being sufficient to forcibly convey the mixture of combustion air and gaseous fuel into the combustion chamber and to forcibly convey the products of combustion through a relatively small exhaust discharge conduit without the need for a draft-type chimney or conduit.
In accordance with still another aspect of the present invention, the combustion air supply sub-system for a heating system includes a separator device, such as a vortex-type separator, that separates combustion air above a predetermined temperature from combustion air that is below such predetermined temperature. Such higher temperature combustion air is conveyed to the combustion chamber of the heating system, and the relatively lower temperature combustion air is conveyed to an exhaust gas heat exchanger for transferring heat from the exhaust gas to such relatively lower temperature combustion air. The combustion air that has been heated in the exhaust gas heat exchanger is then conveyed back to the heated space in order to effectively recover thermal energy that would otherwise have been wasted as the exhaust gas from the combustion chamber is discharged to the atmosphere.
A further aspect of the present invention is the provision of combustion air and gaseous fuel bypass systems, including automatic bypass valves, for bypassing quantities of combustion air and gaseous fuel from the discharges to the intakes of the respective combustion air and gaseous fuel compressors. The bypass systems allow for selective control of the quantities of fuel and air being supplied to the combustion chamber in order to control the heat being supplied to the heated space without the need for the wasteful frequent on/off cycling operation mentioned above in connection with conventional heating systems. In addition, the heating system of the present invention preferably includes a mircoprocessor control system that operates and controls the above bypass systems and other components of the heating system in response to temperature input signals from both the heated space and the exterior surroundings.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.